There are numerous types of fluid warming cassettes. Some of them are disclosed in U.S. Pat. No. 6,464,666 to Augustine; U.S. Pat. No. 5,875,282 to Jordan et al.; U.S. Pat. No. 4,731,072 to Aid; U.S. Pat. No. 4,707,587 to Greenblatt; and U.S. Pat. No. 3,485,245 to Lahr et al.
Lahr et al. disclose a fluid warming cassette. That fluid cassette has an inlet to allow a fluid enter a counter-flow serpentine fluid path. The counter-flow serpentine fluid path is defined in the fluid warming cassette by joining portions of at least two layers of polymeric film together. The fluid exits the fluid warming cassette through at output. Inlet and outlet conduits transport the fluid to the inlet of and from the outlet of the fluid warming cassette. Neither conduit is integrally connected to the fluid warming cassette. The Lahr et al. design had no guide rails because the fluid warming cassette was inserted into a warming unit having an adjustable aperture to receive the fluid warming cassette. See FIGS. 1-4 of U.S. Pat. No. 3,485,245.
Greenblatt discloses an alternative design of a warming cassette and a warming unit. That warming unit had a non-adjustable aperture to receive a fluid warming cassette. Greenblatt's fluid warming cassette is substantially equivalent to Lahr et al.'s fluid warming cassette except Greenblatt has (1) a plurality of holes along the perimeter of the fluid warming cassette and (2) the inlet and outlet are integrally connected to the cassette but not connected to each other. Greenblatt's fluid warming cassette was then attached to a frame unit that was inserted into the non-adjustable aperture of the warming unit. See FIGS. 7, 8, and 10 of U.S. Pat. No. 4,707,587.
Aid discloses a tapered fluid warming cassette. The warming cassette has a top end, a bottom end, and two sides. The length of the top end is greater than the length of the bottom side, hence the cassette is tapered. At the top end, the cassette has an inlet and an outlet tube integrally connected to a quasi-serpentine fluid path. It is a quasi-serpentine path because the fluid path has “short-cuts” for the fluid to go through. Along each side is a sleeve. The sleeve is designed to receive a stiffener device. The stiffener device is shaped in the letter “U” wherein the extensions of the device go into each sleeve at the top end so the remaining portion of the device acts as a handle for the cassette. In addition, the stiffener device is a guide rail for inserting the cassette into a warming unit's narrower, in relation to the apertures of Lahr et al. and Greenblatt, and non-adjustable aperture. The stiffener device, however, is not an integral part of the cassette and can cause problems with removing and inserting the cassette into and out of the aperture of the warming device. One of those problems can be puncturing the cassette. See FIGS. 2, 7 and 10 of U.S. Pat. No. 4,731,072.
The patent which Jordan et al. are listed as the inventors is assigned to the assignee of this application. In particular, Jordan et al. disclose a fluid warming cassette having a counter-flow serpentine fluid path and two independent inlet and outlet nozzles integrally attached to the cassette. The inlet and outlet nozzles act as a stop mechanism to prevent the cassette from being inserted too far into the aperture of the warming unit. Since Jordan et al.'s cassette is thin; the guide rails are integrally attached to the sides of the cassette. A problem with Jordan et al.'s design is that the cassette is too flimsy and difficult to insert into the warming unit's aperture. See FIG. 3 of U.S. Pat. No. 5,875,282.
Augustine attempts to solve Jordan et al.'s flimsiness issue. Augustine's attempt requires placing a quadrilateral frame structure onto the perimeter of a fluid cassette. That quadrilateral frame must have (1) a stop mechanism positioned at the top end that prevents further insertion of the cassette into the aperture of a warming unit, and (2) guide rails to help assist the cassette into the aperture. In any case, Augustine's frame unit creates further problems. First, it does not solve the insertion problem because the quadrilateral shape is sometimes difficult to align with warming unit's aperature. Second, it requires an expanded aperture of the warming unit to accommodate the quadrilateral frame. By expanding the aperture, the effectiveness of the warming unit is slightly diminished. See FIGS. 1B and 2A of U.S. Pat. No. 6,464,666.
After reviewing these references, we noticed that the bottom end of each fluid warming cassette has two squared or nearly squared corners. That means, the bottom end is essentially parallel to the top end and perpendicular to the other sides. It is our understanding that the bottom end has this shape so the cassette remains within the warming unit.
The present invention has a unique design which solves the flimsiness and insertion problems of Jordan et al. and the other cited references.